Process for producing depsipeptide derivatives and novel intermediates therefor

ABSTRACT

An industrially excellent alternative process for producing cyclodepsipeptide derivatives, as represented in formula (1), having an excellent vermicidal activity as an animal and human anthelmintic, wherein R 1  represents hydrogen or a hydroxyl-protective group; R 2  represents a carboxyl group optionally protected; R 3 , R 4 , R 7  and R 8  represent each a lower alkyl, aryl or (un)substituted aralkyl; and R 5 , R 6 , R 9  and R 10  represent each a lower alkyl.

TECHNICAL FIELD

This invention relates to an alternative process for producing acyclodepsipeptide derivative having vermicidal activity and to novelintermediates for synthesis of said depsipeptide derivative.

BACKGROUND ART

The cyclodepsipeptide derivative of this invention, represented by thefollowing general formula (I), is known to be a compound having highvermicidal activity and finds application as an anthelmintic in animalsand man. In the conventional synthesis of such cyclodepsipeptides, thecyclization reaction involved is invariably carried out in the manner ofamide bond formation to construct a cyclic structure (WO 93/19053, KokaiTokkyo Koho H5-320148, EP-626375, EP-626376).

For example, a cyclization process using the following route is known(WO 93/19053).

Conventional Route:

DISCLOSURE OF INVENTION

The inventors of this invention studied the possible cyclizationreaction by ester bond formation in the production process for suchcyclodepsipeptides and have developed this instant invention.

The depsipeptide of this invention can be represented by the followinggeneral formula (I).

In accordance with this invention, the objective compound (I) or itssalt can be produced by a process involving the following series ofsteps.

[In the respective formulas, R₁ represents hydrogen or ahydroxyl-protecting group; R₂ represents a carboxyl group or a protectedcarboxyl group; R₃, R₄, R₇ and R₉ each represents a lower alkyl group,an aryl group, or a substituted or unsubstituted aralkyl group; R₅, R₆,R₉ and R₁₀ each represents a lower alkyl group; R₁₁ represents hydrogenor an amino-protecting group]

Compound (II) in the above process includes known compounds and novelcompounds, and compounds (IV), (VII) and (VIII), inclusive of theirreactive derivatives, as well as salts thereof are novel compounds.

Throughout this specification, amino acids, peptides, protective groups,condensing agents, etc. are indicated by using the abbreviationsrecommended by IUPAC-IUB (a committee on biochemical nomenclature) whichare in common use.

Moreover, the amino acids and their residues as indicated by suchabbreviations mean the L-configured compounds and residues unlessotherwise specified, and D-configured compounds and residues areindicated by the symbol D-.

The abbreviations used in the invention are as follows.

MeLeu: methylleucine

p-MorPhLac: 2-hydroxy-3-(4-morpholinophenyl)-propionic acid[β-(p-morpholinophenyl)lactic acid]

Lac: 2-hydroxypropionic acid [lactic acid]

MOM: methoxymethyl

Boc: t-butoxycarbonyl

Bzl: benzyl

The preferred salts of Compounds (I), (II), (III), (IV), (V), (VI),(VII) and (VIII) include conventional nontoxic salts, which are saltswith various bases and acid addition salts. More particularly, there canbe mentioned salts with inorganic bases, such as alkali metals (e.g.sodium salt, potassium salt, cesium salt, etc.) and alkaline earthmetals (e.g. calcium salt, magnesium salt, etc.), and ammonium salts;salts with organic bases, such as organic amine salts (e.g.triethylamine salt, pyridine salt, picoline salt, ethanolamine salt,triethanolamine salt, dicyclo-hexylamine salt,N,N′-dibenzylethylenediamine salt, etc.); inorganic acid addition salts(e.g. hydro-chloride, hydrobromide, sulfate, phosphate, etc.); organiccarboxylic acid addition salts or organic sulfonic acid addition salts(e.g. formate, acetate, trifluoroacetate, maleate, tartrate,methanesulfonate, benzenesulfonate, p-toluenesulfonate, etc.); and saltswith basic or acidic amino acids (e.g. arginine salt, aspartate,glutamate, etc.).

The preferred examples and the explanations of the various definitionsmade in the foregoing as well as the following disclosure and fallingunder the scope of the invention are now given in detail.

The preferred “hydroxyl-protecting group” includes but is not limited toacyl, substituted or unsubstituted aralkyl, which will be described indetail hereinafter, lower alkoxy(lower)alkyl, carbamoyl and silyl.

The preferred examples of the “acyl” mentioned just above are aliphaticacyl groups and acyl groups having an aromatic ring or heterocycle. Thepreferred examples of such acyl include but are not limited to:

lower alkanoyl groups such as formyl, acetyl, propionyl, butyryl,isobutyryl, valeryl, isovaleryl, oxalyl, succinyl, pivaloyl, etc.;

lower alkoxycarbonyl groups such as methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, 1-cyclopropylethoxycarbonyl, isopropoxycarbonyl,butoxycarbonyl, t-butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl,etc.;

lower alkanesulfonyl groups such as mesyl, ethanesulfonyl,propanesulfonyl, isopropanesulfonyl, butanesulfonyl, etc.;

aroyl groups such as benzoyl, toluoyl, xyloyl, naphthoyl, phthaloyl,indancarbonyl, etc.;

ar(lower)alkanoyl groups such as phenylacetyl, phenylpropionyl, etc.;and

ar(lower)alkoxycarbonyl groups such as benzyloxycarbonyl,phenethyloxycarbonyl, etc.

The above-mentioned acyl groups may each have one or more suitablesubstituent groups such as chlorine, bromine, fluorine and iodine.

The preferred examples of said lower alkoxy(lower)alkyl are1-methyl-1-methoxyethyl, methoxy-methyl and methoxypropyl, among others.

The preferred “protected carboxyl” includes esterified carboxyl such asthe following “esterified carboxyl” groups. The preferred ester moietyof such esterified carboxyl includes lower alkyl esters optionallycontaining one or more suitable substituent groups. For example, therecan be mentioned lower alkyl esters such as methyl ester, ethyl ester,propyl ester, isopropyl ester, butyl ester, isobutyl ester, tert-butylester, pentyl ester, tert-pentyl ester, hexyl ester, etc.; loweralkanoyloxy(lower)alkyl esters such as acetoxymethyl ester,propionyloxymethyl ester, butyryloxymethyl ester, valeryloxymethylester, pivaloyloxymethyl ester, hexanoyloxymethyl ester, etc.; mono(ordi- or tri-)halo(lower)alkyl esters such as 2-iodoethyl ester,2,2,2-trichloroethyl ester, etc.; lower alkenyl esters such as vinylester, allyl ester, etc.; ar(lower)alkyl esters optionally having one ormore substituent groups, such as benzyl ester, 4-methoxybenzyl ester,4-nitrobenzyl ester, phenethyl ester, trityl ester, benzhydryl ester,bis(methoxy-phenyl)methyl ester, 3,4-dimethoxybenzyl ester,4-hydroxy-3,5-di-tert-butylbenzyl ester, etc.

The protective group for said “protected carboxyl” includes thoseprotective groups which are conventionally used for temporary protectionof carboxyl groups in the field of amino acid or peptide chemistry.

The “lower” means the range of 1˜6 carbon atoms, preferably 1˜4 carbonatoms, unless otherwise specified.

The preferred “lower alkyll” includes straight-chain or branched-chainalkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl,isobutyl, tert-butyl, pentyl, neopentyl and hexyl.

The preferred “aryl” includes but is not limited to phenyl, naphthyl,and lower alkyl-substituted phenyl (e.g. tolyl, mesityl, cumenyl, xylyl,diethylphenyl, diisopropylphenyl, di-tert-butylphenyl, etc.).

The “substituted or unsubstituted aralkyl” means said lower alkyl grouphaving an aryl group in an arbitrary position and includes benzyl,phenethyl, 3-phenylpropyl, benzhydryl, and trityl, to mention a fewpreferred examples.

The “aralkyl” for R₃, R₇ may have 1 or more substituent groups.

The preferred substituent groups for “substituted benzyl”, among said“substituted or unsubstituted aralkyl”, includes but is not limited tohydroxyl, lower alkoxy, lower alkoxy(lower)alkoxy, loweralkoxy-(lower)alkoxy(lower)alkoxy, heterocyclic(lower)-alkoxy, loweralkyl, amino, mono- or di-substituted lower alkylamino, cyclic amino,nitro, and halogen such as fluorine, chlorine, bromine or iodine. One ormore of such substituent groups may be present.

The above preferred “lower alkoxy” includes but is not limited tomethoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, pentyloxy,isopentyloxy, and hexyloxy.

The above preferred “lower alkoxy(lower)alkoxy” includes but is notlimited to methoxymethoxy, methoxyethoxy, methoxypropoxy, andethoxyisopropoxy.

The above preferred “lower alkoxy(lower)-alkoxy(lower)alkoxy” includesbut is not limited to methoxymethoxyethoxy, methoxyethoxyethoxy,methoxyethoxypropoxy, and ethoxymethoxyisopropoxy.

The above preferred “heterocyclic(lower)alkoxy” includes but is notlimited to pyridylmethoxy and furanylmethoxy.

The above preferred “mono- or di-substituted lower alkylamino” is agroup derived from a lower alkylamino group by substitution with 1 or 2lower alkyl groups such as methyl, ethyl, isopropyl, t-butyl, t-pentyl,etc., thus including methylamino, ethylamino, dimethylamino,diethylamino, di-n-propylamino, diisopropylamino, and dibutylamino, tomention just a few preferred examples.

The above preferred “cyclic amino” is an aromatic or alicyclic grouphaving at least one nitrogen atom as the hetero-atom and may be eithersaturated or unsaturated and either monocyclic or fused polycyclic.Moreover, it may contain one or more additional hetero-atoms such asnitrogen, oxygen, sulfur, etc. within the ring. In addition, this cyclicamino group may be a spiro ring group or a bridged ring group. Althoughthere is no particular limitation on the number of constituent atoms,this cyclic amino may for example be a 3- through 8-membered ring in thecase of a monocyclic system or a 7- through 11-membered ring in the caseof a bicyclic system.

As examples of the cyclic amino, there can be mentioned saturated orunsaturated monocyclic groups having one nitrogen atom as thehetero-atom, such as 1-azetidinyl, pyrrolidino, 2-pyrrolin-1-yl,1-pyrrolyl, piperidino, 1,4-dihydropyridin-1-yl,1,2,5,6-tetrahydropyridin-1-yl, homopiperidino, etc.; saturated orunsaturated monocyclic groups containing 2 or more nitrogen atoms as thehetero-atoms, such as 1-imidazolidinyl, 1-imidazolyl, 1-pyrazolyl,1-triazolyl, 1-tetrazolyl, 1-piperazinyl, 1-homopiperazinyl,1,2-dihydropyridazin-1-yl, 1,2-dihydropyrimidin-1-yl,perhydropyrimidin-1-yl, 1,4-diazacycloheptan-1-yl, etc.; saturated orunsaturated monocyclic groups containing 1˜3 nitrogen atoms and 1˜2oxygen atoms as the hetero-atoms, such as oxazolidin-3-yl,2,3-dihydroisoxazol-2-yl, morpholino, etc.; saturated or unsaturatedmonocyclic groups containing 1˜3 nitrogen atoms and 1˜2 sulfur atoms asthe hetero-atoms, such as thiazolidin-3-yl, iso-thiazolin-2-yl,thiomorpholino, etc.; fused cyclic groups such as indol-1-yl,1,2-dhydrobenzimidazol-1-yl, perhydrospiro[1,2-a]pyrazin-2-yl, etc.;spiro ring groups such as 2-azaspiro[4,5]decan-2-yl etc.; and bridgedheterocyclic groups such as 7-azabicyclo-[2,2,1]heptan-7-yl, amongothers.

The above-mentioned “cyclic amino which may be substituted” includespyrrolizino, morpholino, 1-piperazino, 4-methylpiperazino andpiperidino, to mention just a few preferred specific examples.

The “amino-protecting group” includes acyl groups, for example loweralkanoyl groups such as formyl, acetyl, propionyl, pivaloyl, hexanoyl,etc., mono(or di- or tri-) halo (lower) alkanoyl groups such aschloroacetyl, bromoacetyl, dichloroacetyl, trifluoroacetyl, etc., loweralkoxycarbonyl groups such as methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, t-butoxycarbonyl, t-pentyloxycarbonyl,hexyloxycarbonyl, etc., carbamoyl, aroyl groups such as benzoyl,toluoyl, naphthoyl, etc., ar(lower)alkanoyl groups such as phenylacetyl,phenylpropionyl, etc., aryloxycarbonyl groups such as phenoxycarbonyl,naphthyloxycarbonyl, etc., aryloxy(lower)alkanoyl groups such asphenoxyacetyl, phenoxypropionyl, etc., arylglyoxyloyl groups such asphenylglyoxyloyl, naphthylglyoxyloyl, etc., and optionally substitutedar(lower)alkoxycarbonyl groups such as benzyloxycarbonyl,phenethyloxycarbonyl, p-nitrobenzyloxycarbonyl, etc., among others;substituted or unsubstituted ar(lower)alkylidene groups such asbenzylidene, hydroxybenzylidene etc.; and ar(lower)alkyl groups such asmono(or di- or tri-)phenyl (lower) alkyl groups, e.g. benzyl, phenethyl,benzhydryl, trityl, etc.

Among the above-mentioned amino-protecting groups are those protectivegroups which are conventionally used for provisional protection of aminogroups in amino acid or peptide chemistry.

The process for producing the objective compound (I) is now described indetail.

Process

Step 1

Compound (IV) or a salt thereof can be produced by reacting compound(II) or a reactive derivative of its carboxyl group, or a salt thereof,with compound (III) or a reactive derivative of its amino group or asalt thereof.

This reaction can be conducted in the conventional manner to convert thecarboxyl group to the amide bond:

The preferred reactive derivative of the carboxyl group of compound (II)includes acid halides, acid anhydrides, activated amides, activatedesters, etc. The preferred examples are the acid chloride; acid azide;mixed acid anhydrides with such acids as substituted phosphoric acids(e.g. dialkyl phosphate, phenyl phosphate, diphenyl phosphate, dibenzylphosphates halophosphoric acids, etc.), dialkyl phosphite, sulfurousacid, thiosulfuric acid, sulfuric acid, alkyl carbonates, loweralkanesulfonic acids (e.g. methanesulfonic acid, ethanesulfonic acid,etc.), aliphatic carboxylic acids (e.g. acetic acid, propionic acid,butyric acid, isobutyric acid, pivalic acid, pentanoic acid,isopentanoic acid, 2-ethylbutyric acid, trichloroacetic acid, etc.) oraromatic carboxylic acids (e.g. benzoic acid etc.); symmetric acidanhydride; active amides with imidazole, 4-substituted imidazole,dimethylpyrazole, triazole or tetrazole; and esters such as activeesters (e.g. cyanomethyl ester, methoxymethyl ester,dimethyliminomethyl[ (CH₃)₂N⁺=CH—] ester, vinyl ester, propargyl ester,p-nitrophenyl ester, 2,4-dinitrophenyl ester, trichlorophenyl ester,pentachlorophenyl ester, pentafluorophenyl ester, mesylphenyl ester,phenylazophenyl ester, phenylthio ester, p-nitrophenylthio ester,p-cresylthio ester, carboxymethylthio ester, pyranyl ester, pyridylester, piperidyl ester, 8-quinolylthio ester, etc.), and esters withN-hydroxyl compounds (e.g. N,N-dimethylhydroxylamine,1-hydroxy-2-(1H)-pyridone, N-hydroxysuccinimide, N-hydroxyphthalimide,1-hydroxy-1H-benzotriazole, etc.). Those reactive derivatives can beselectively used according to the species of compound (II).

The preferred reactive derivative of the amino group of compound (III)includes Schiff base-type imine and enamine tautomers which can beobtained by reacting compound (III) with carbonyl compounds such asaldehydes or ketones; silyl derivatives which can be obtained byreacting compound (III) with silyl compounds such asbis(trimethylsilyl)acetamide, mono(trimethylsilyl)acetamide,bis(trimethylsilyl)-urea, etc.; and the derivative which can be obtainedby reacting compound (III) with phosphorus trichloride or phosgene.

This reaction is generally conducted in the common solvent such aswater, alcohol (e.g. methanol, ethanol, etc.), acetone, dioxane,tetrahydrofuran, acetonitrile, chloroform, dichloromethane, ethylenechloride, ethyl acetate, N,N-dimethylformamide, pyridine, etc., or anorganic solvent, other than the above, which does not interfere with thereaction. Among those solvents, hydrophilic solvents can be used inadmixture with water.

There is no particular limitation on the reaction temperature but thereaction is generally carried out under cooling, at room temperature orat elevated temperature.

When compound (II) is used either in its free form or in the salt formin conducting this reaction, the reaction is preferably carried out inthe presence of a conventional condensing agent. The condensing agentincludes but is not limited to carbodiimides and salts thereof (e.g.N,N′-dicyclohexylcarbodiimide,N-cyclohexyl-N′-morpholinoethylcarbodiimide,N-cyclo-hexyl-N′-(4-diethylaminocyclohexyl)carbodiimide,N,N′-diethylcarbodiimide, N,N′-diisopropylcarbodi-imide,N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide or its hydrochloride,diphenylphosphoryl azide, diethylphosphoryl cyanide,bis(2-oxo-3-oxazolidin-yl)phosphinic chloride, etc.); triazoles (e.g.1-(p-chlorobenzenesulfonyloxy)-6-chloro-1H-benzotriazole,N-hydroxybenzotriazole, etc.); imidazoles (e.g.N,N′-carbonyldiimidazole, N,N′-carbonylbis(2-methylimidazole), etc.;ketenimine compounds (e.g. pentamethyleneketene-N-cyclohexylimine,diphenylketene-N-cyclohexylimine, etc.); ethoxyacetylene,1-alkoxy-1-chloroethylenes; trialkyl phosphites; polyethyl phosphate;polyisopropyl phosphate; phosphorus oxychloride (phosphoryl chloride);diphenyl phosphorochloridate; triphenylphosphine; phosphorustrichloride; thionyl chloride; oxalyl chloride; halopyridinium salts(e.g. 2-chloro-1-methylpyridinium iodide etc.); cyanuric chloride; loweralkyl haloformates (e.g. ethyl chloroformate, isopropyl chloroformate,etc.); 2-ethyl-7-hydroxybenzisoxazolium salts;2-ethyl-5-(m-sulfophenyl)isoxazolium hydroxide internal salt; Vilsmeierreagents prepared by reacting N,N-dimethylformamide with thionylchloride, phosgene, trichloromethyl chloroformate, phosphorusoxychloride, etc., respectively.

This reaction can also be conducted in the presence of an inorganic ororganic base, for example alkali metal hydroxides (e.g. sodiumhydroxide, potassium hydroxide, etc.), alkali metal carbonates (e.g.sodium carbonate, potassium carbonate, etc.), alkali metalhydrogen-carbonates (e.g. sodium hydrogencarbonate, potassiumhydrogencarbonate, etc.), tri (lower) alkylamines (e.g. trimethylamine,triethylamine, etc.), pyridine and its derivatives (e.g.N,N-dimethylaminopyridine, 4-pyrrolidinopyridine, 4-piperazinopyridine,4-(4-methylpiperidino)pyridine, etc. and their hydrochlorides,hydrobromides, etc.), N-(lower)alkylmorpholines (e.g. N-methylmorpholineetc.), and N,N-di(lower)alkylbenzylamines, and so on.

Step 2

Compound (VII) or a salt thereof can be produced by reacting compound(V) or a reactive derivative of the carboxyl group thereof, or a saltthereof, with compound (VI) or a reactive derivative of the amino groupthereof, or a salt thereof.

This reaction can be carried out substantially in the same manner as thereaction in Step 1. Therefore-, with regard to the procedure andconditions (e.g. solvent, reaction temperature, etc.) of this reaction,reference should be made to the description of Step 1.

Step 3

Compound (VIII) or a salt thereof can be produced by reacting compound(VII) or a reactive derivative of the amino group thereof, or a saltthereof, with compound (IV) or a reactive derivative of the carboxylgroup thereof, or a salt thereof.

This reaction can be carried out substantially in the same manner as thereaction in Step 1. Therefore, with regard to the procedure andconditions (e.g. solvent, reaction temperature, etc.) of this reaction,reference should be made to the description of Step 1.

Step 4

Compound (I) or a salt thereof can be produced by subjecting compound(VIII) or a reactive derivative of its carboxyl group, or a saltthereof, to cyclization reaction.

The preferred reactive derivative of the carboxyl group of compound(VIII) includes the same species as those mentioned by way of example inthe description of Step 1.

This reaction is carried out by the conventional method for cyclization,for example under heating or in the presence of a condensing agent. Thepreferred condensing agent includes the same substances as mentioned byway of example in the description of Step 1.

This reaction can also be conducted in the presence of an inorganic ororganic base, for example alkali metal hydroxides (e.g. sodiumhydroxide, potassium hydroxide, etc.), alkali metal carbonates (e.g.sodium carbonate, potassium carbonate, etc.), alkali metalhydrogencarbonates (e.g. sodium hydrogencarbonate, potassiumhydrogencarbonate, etc.), tri(lower)alkylamines (e.g. trimethylamine,triethylamine, etc.), pyridine and its derivatives (e.g.N,N-dimethylaminopyridine, 4-pyrrolidinopyridine, 4-piperazinopyridine,4-(4-methylpiperidino)pyridine, and their hydrochlorides, hydrobromides,etc.), N-(lower)alkylmorpholines (e.g. N-methylmorpholine etc.), andN,N-di(lower)alkylbenzylamines, and so on.

This reaction in the presence of a condensing agent is generally carriedout in the common solvent such as chloroform, tetrahydrofuran,N,N-dimethylformamide, alcohol (e.g. methanol, ethanol, propanol, etc.),acetonitrile, pyridine, 4-methyl-2-pentanone, benzene, toluene, xylene,etc., a mixture of such solvents, or an arbitrary other organic solventwhich does not interfere with the reaction.

There is no particular limitation on the reaction temperature but thereaction is usually carried out under cooling, at room temperature, orat elevated temperature.

The cyclization reaction under heating can be carried out in saidorganic solvent under heating at a temperature not exceeding the boilingpoint of the solvent.

When R₁, R₂ and R₁₁ of compounds (IV), (VII), (VIII) and their saltshave been protected, the hydroxyl-protecting group, carboxyl-protectinggroup or amino-protecting group may be eliminated by a deprotectionreaction.

The deprotection reaction is carried out by the routine procedure forremoving a hydroxyl-protecting group, a carboxyl-protecting group or anamino-protecting group, for example by hydrolysis or reduction.

The hydrolysis is preferably carried out in the presence of a base or anacid (inclusive of a Lewis acid)

The preferred base includes inorganic and organic bases such as alkalimetals (e.g. sodium, potassium, etc.), alkaline earth metals (e.g.magnesium, calcium, etc.), the hydroxides, carbonates orhydrogen-carbonates of said metals, alkali metal alkoxides (e.g. sodiummethoxide, sodium ethoxide, potassium t-butoxide, etc.), alkali metalacetates, alkaline earth metal phosphates, alkali metalhydrogenphosphates (e.g. disodium hydrogenphosphate, dipotassiumhydrogenphosphate, etc.), tri(lower)alkylamines (e.g. trimethylamine,triethylamine, etc.), pyridine and its derivatives (e.g. picoline,lutidine, 4-dimethyl-aminopyridine, etc.), N-(lower)alkylmorpholines(e.g. N-methylmorpholine etc.), 1,5-diazabicyclo[4.3.0]-non-5-ene,1,4-diazabicyclo[2.2.2]octane, 1,8-diazabicyclo[5.4.0]undec-7-ene, andquinoline, among others.

The preferred acid includes organic acids (e.g. formic acid, aceticacid, propionic acid, trichloroacetic acid, trifluoroacetic acid, etc.)and inorganic acids (e.g. hydrochloric acid, hydrobromic acid, sulfuricacid, etc.) The deprotection reaction using a trihaloacetic acid (e.g.trichloroacetic acid, trifluoroacetic acid, etc.) can be accelerated byadding a cation scavenger (e.g. phenol, anisole, etc.).

This hydrolysis reaction is generally conducted in the common solventsuch as water, alcohol (e.g. methanol, ethanol, etc.), diethyl ether,dioxane, tetrahydrofuran, dichloromethane, ethyl acetate, etc., amixture of such solvents, or a suitable other organic solvent that doesnot interfere with the reaction. When the above-mentioned base or acidis a liquid, the base or acid may be used as the solvent as well.

There is no particular limitation on the reaction temperature but thereaction is generally conducted under cooling, at room temperature, orat elevated temperature.

The reduction method which can be applied to the deprotection reactionincludes chemical reduction and catalytic reduction.

The preferred reducing agent which can be used in chemical reductionincludes but is not limited to various combinations of a metal (e.g.tin, zinc, iron, etc.) or a metal compound (e.g. chromium chloride,chromium acetate, etc.) with an organic or inorganic acid (e.g. formicacid, acetic acid, propionic acid, trifluoroacetic acid,p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, etc.).

The preferred catalyst which can be used for the catalytic reductionincludes but is not limited to the common catalysts such as platinumcatalysts (e.g. platinum plate, platinum sponge, platinum black,colloidal platinum, platinum oxide, platinum wire, etc.), palladiumcatalysts (e.g. palladium sponge, palladium black, colloidal palladium,palladium oxide, palladium-carbon, palladium-barium sulfate,palladium-barium carbonate, etc.), nickel catalysts (e.g. reducednickel, nickel oxide, Raney nickel, etc.), cobalt catalysts (e.g.reduced cobalt, Raney cobalt, etc.), iron catalysts (e.g. reduced ion,Raney ion, etc.), and copper catalysts (e.g. reduced copper, Raneycopper, Ullmann copper, etc.).

The reduction reaction is generally carried out in a solvent which doesnot interfere with the reaction, such as water, alcohol (e.g. methanol,ethanol, propanol, etc.), N,N-dimethylformamide, etc., or a mixture ofsuch solvent. When the above-mentioned acid for use in chemicalreduction is a liquid, the acid can be used as the solvent as well. Thepreferred solvent for catalytic reduction includes not only theabove-mentioned solvents but also such common solvents as diethyl ether,dioxane, tetrahydrofuran, etc. and mixtures thereof.

There is no particular limitation on the reaction temperature for thisreduction but the reduction reaction is generally conducted undercooling, at room temperature, or at elevated temperature.

The compounds obtained in the respective production steps describedabove can be separated and purified by the conventional procedures suchas, for example, extraction, precipitation, recrystallization, columnchromatography, and recrystallization.

The starting compounds to be used in the above respective steps can beprepared by the processes described hereinafter in production examples.

While compound (I) through compound (VIII) may include one or morestereoisomers due to asymmetric carbon, such isomers and mixturesthereof also fall within the scope of the invention.

The depsipeptide derivative (I) and its pharmaceutically acceptable saltinclude solvates [for example inclusion compounds (e.g. hydrates,etc.)].

In accordance with this invention there is provided a commerciallyadvantageous alternative process for producing the cyclodepsipeptidederivative (I), a compound having high vermicidal activity for use as ananthelmintic in animals and man.

The following production examples and examples illustrate this inventionin further detail.

PRODUCTION EXAMPLE 1

Diisopropylethylamine (1.15 ml) and chloromethyl methyl ether (0.5 ml)were added to a solution of benzyl(R)-2-hydroxyl-3-(4-morpholinophenyl)propionate (1.5 g) indichloromethane (15 ml) under ice-cooling and the mixture was stirred atroom temperature for 19 hours. This reaction mixture was diluted withwater (40 ml) and extracted with ethyl acetate (20 ml×3). The organiclayer was washed serially with 5% sodium hydrogencarbonate solution (20ml), water (20 ml) and saturated aqueous solution of sodium chloride (20ml) in the order mentioned and dehydrated over anhydrous sodium sulfateand the solvent was then distilled off under reduced pressure. Theresulting crude product was purified by silica gel columnchromatography, elution being carried out with hexane-ethyl acetate(1:2, v/v). From the fraction containing the objective compound, thesolvent was distilled off under reduced pressure to provide 1.73 g ofbenzyl (R)-2-methoxymethoxy-3-(4-morpholinophenyl)propionate.

¹H-NMR (CDCl₃; δ): 2.84-3.10 (2H, m), 3.07-3.19 (4H, m), 3.13 (3H, s),3.80-3.94 (4H, m), 4.32 (1H, dd), 4.53 (1H, d), 4.64 (1H, d), 5.14 (2H,s), 6.81 (2H, d), 7.12 (2H, d), 7.23-7.41 (5H, m) APCI-MS (M+H)⁺=386

PRODUCTION EXAMPLE 2

To a solution of benzyl(R)-2-methoxymethoxy-3-(4-morpholinophenyl)propionate (1.66 g) inmethanol (8.6 ml) was added 10% palladium-carbon (0.2 g), andhydrogenation was carried out in a hydrogen atmosphere at atmosphericpressure and room temperature for 100 minutes. After the catalyst wasfiltered off, the solvent was distilled off under reduced pressure. Theresidue was further subjected to azeotropic distillation with isopropylether-hexane to provide 1.44 g of(R)-2-methoxymethoxy-3-(4-morpholino-phenyl)propionic acid.

¹H-NMR (CDCl₃; δ): 2.88-3.10 (2H, m), 3.08-3.10 (4H, m), 3.17 (3H, s),3.78-3.92 (4H, m), 4.34 (1H, dd) 4.52 (1H, d), 4.66 (1H, d), 6.86 (2H,d), 7.18 (2H, d)

EXAMPLE 1

To a mixture of MOM-D-p-MorPhLac-OH (1.18 g), H-MeLeu-D-Lac-OBzl (0.87g), N-methylmorpholine (1.06 ml) and acetonitrile (15 ml) was addeddiphenyl phosphorochloridate (1.29 g) under ice-cooling, and the mixturewas stirred under the same conditions for 90 minutes. The solvent wasthen distilled off under reduced pressure and the residue was dilutedwith water (40 ml) and extracted with isopropyl ether (20 ml×3). Theisopropyl ether layer was serially washed with 5% sodiumhydrogencarbonate solution (20 ml), water (20 ml) and saturated aqueoussolution of sodium chloride (20 ml) in the order mentioned anddehydrated over anhydrous sodium sulfate. After the sodium sulfate wasfiltered off, the filtrate was passed through silica gel (2 g) and thesolvent was distilled off under reduced pressure to provide 2.08 g ofMOM-D-p-MorPhLac-MeLeu-D-Lac-OBzl.

¹H-NMR (CDCl₃; δ): 0.86 (6H, d), 1.46 (3H, d), 1.41-1.80 (3H, m),2.78-3.02 (5H, m), 3.05-3.22 (7H, m), 3.78-3.93 (4H, m), 4.42-4.77 (3H,m), 5.01-5.20 (3H, m), 5.38-5.51 (1H, m), 6.87 (2H, d), 7.18 (2H, d),7.20-7.40 (5H, m) APCI-MS (M+H)⁺=585

EXAMPLE 2

Using MOM-D-p-MorPhLac-MeLeu-D-Lac-OBzl (2.06 g) in lieu of benzyl(R)-2-methoxymethoxy-3-(4-morpholinophenyl)propionate, the procedure ofProduction Example 2 was otherwise repeated to provide 1.72 g ofMOM-D-p-MorPhLac-MeLeu-D-Lac-OH.

¹H-NMR (CDCl₃; δ): 0.87 (3H, d); 0.88 (3H, d), 1.49 (3H, d), 1.50-1.93(3H, m), 2.78-3.30 (12H, m), 3.80-3.96 (4H, m), 4.50-4.80 (3H, m), 5.10(1H, dd), 5.31 (1H, dd), 6.87 (2H, d), 7.17 (2H, d)

EXAMPLE 3

Using Boc-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-OH (2.48 g) in lieu ofMOM-D-p-MorPhLac-OH and HCl.H-MeLeu-OBzl (0.95 g) in lieu ofH-MeLeu-D-Lac-OBzl, the procedure of Example 1 was otherwise repeated toprovide 4.05 g of Boc-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OBzl.

¹H-NMR (CDCl₃; δ): 0.78-1.03 (18H, m), 1.2-1.98 (21H, m), 2.73-3.20(15H, m), 3.80-3.97 (4H, m), 4.63-4.80 (m) & 4.91-5.04 (m) & 5.10-5.34(m) (7H), 6.86 (2H, d), 7.15 (2H, d), 7.20-7.40 (5H, m) FAB-MS(M−Boc+H)⁺=795

EXAMPLE 4

In 4N hydrogen chloride in ethyl acetate (18 ml) was dissolved 4.04 g ofBoc-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OBzl under ice-cooling, and themixture was stirred under the same conditions for 1 hour. The solventwas then distilled off under reduced pressure and the residue wassubjected twice to azeotropic distillation with ethyl acetate-toluene toprovide 4.16 g of 2HCl.H-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OBzl.

¹H-NMR (CDCl₃; δ) 0.78-1.10 (18H, m), 1.22-2.00 (12H, m), 2.58-3.34(11H, m), 3.38-3.58 (4H, m), 3.76-3.92 (1H, m), 4.13-4.41 (4H, m),4.58-4.77 (m) & 4.97-5.63 (m) (6H), 7.10-7.42 (5H, m)), 7.47 (2H, d),7.74 (2H, d), 9.35-9.60 (1H, m), 10.14-10.50 (1H, m)

EXAMPLE 5

To a mixture of MOM-D-p-MorPhLac-MeLeu-D-Lac-OH (1.71 g),2HCl.H-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OBzl (4.15 g),N-methylmorpholine (1.54 ml) and acetonitrile (14 ml) was added diphenylphosphorochloridate (0.9 g) under ice-cooling, and the whole mixture wasstirred under the same conditions for 3 hours. Then, N-methylmorpholine(0.18 ml) and diphenyl phosphorochloridate (0.45 g) were further addedand the mixture was stirred as it was for 30 minutes. The solvent wasthen distilled off under reduced pressure and the residue was dilutedwith water (40 ml) and extracted with ethyl acetate (20 ml×3). The ethylacetate layer was serially washed with 5% sodium hydrogen carbonatesolution (20 ml), water (20 ml) and saturated aqueous solution of sodiumchloride (20 ml) in the order mentioned and dehydrated over anhydroussodium sulfate and the solvent was distilled off under reduced pressure.The residual crude product was purified by silica gel columnchromatography, elution being carried out with hexane-ethylacetate-ethanol (55/40/5, v/v/v). From the fraction containing theobjective product, the solvent was distilled off under reduced pressureto provide 3.39 g ofMOM-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLou-OBzl.

¹H-NMR (CDCl₃; δ) 0.70-1.03 (24H, m), 1.03-1.92 (18H, m), 2.72-3.21(27H, m), 3.72-3.95 (8H, m), 4.36-4.81 (m) & 4.96-5.05 (m) & 5.05-5.56(m) (12H), 6.82 (4H, d), 7.03-7.42 (9H, m). FAB-MS (M+H)⁺=1271

EXAMPLE 6

UsingMOM-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OBzl(0.21 g) in lieu of benzyl(R)-2-methoxymethoxy-3-(4-morpholinophenyl)-propionate, the procedure ofProduction Example 2 was otherwise repeated to provide 0.18 g ofMOM-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OH.

¹H-NMR (CDCl₃; δ): 0.72-1.04 (24H, m), 1.04-1.91 (18H, m), 2.71-3.21(27H, m), 3.79-3.97 (8H, m), 4.37-4.81 (m) & 4.90-5.60 (m) (10H), 6.82(4H, d) 7.08-7.30 (4H, m) FAB-MS (M+Na)⁺=1202

EXAMPLE 7

To a solution ofMOM-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OH(0.45 g) in dichloromethane (2.5 ml) was added trifluoroacetic acid (2.5ml) under ice-cooling, and the mixture was stirred as it was for 18hours. The solvent was then distilled off under reduced pressure. Then,ethyl acetate (20 ml) and water (20 ml) were added to the residue andits pH was adjusted to 7 with 5% sodium hydrogencarbonate. After theethyl acetate layer was separated, the aqueous layer was extracted withethyl acetate (20 ml×2) The organic layers were combined, washed withsaturated aqueous solution of sodium chloride (20 ml) and dehydratedover anhydrous sodium sulfate. The solvent was then distilled off underreduced pressure to provide 0.46 g ofH-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OH.

¹H-NMR (CDCl₃; δ): 0.70-1.05 (24H, m), 1.16-1.90 (18H, m), 2.70-3.36(24H, m), 3.78-3.92 (8H, m), 4.50-4.78 (m) & 4.83-5.01 (m) & 5.18-5.56(m) (8H) 6.79-6.94 (4H, m), 7.03-7.21 (4H, m) FAB-MS (M+H+Na)⁺=1159

EXAMPLE 8

To ethanol-free chloroform (43.7 ml) were added dicyclohexylcarbodiimide(162.8 mg), dimethylaminopyridine (145.4 mg) and dimethylaminopyridinehydrochloride (125.1 mg), followed by refluxing at 75° C. To thismixture was added a solution ofH-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-D-p-MorPhLac-MeLeu-D-Lac-MeLeu-OH (448mg) in chloroform (9 ml) over 4.5 hours, and the mixture was furtherrefluxed for 3.5 hours. Then, cyclohexylcarbodiimide (80 mg) was furtheradded and the mixture was refluxed for 1 hour, followed by furtheraddition of dicyclohexylcarbodiimide (80 mg), and the mixture wasfurther refluxed for 1.5 hours. After the solvent was distilled offunder reduced pressure, water (20 ml) and ethyl acetate (20 ml) wereadded to the residue and-the insoluble matter was filtered off. Afterthe ethyl acetate layer was separated from the aqueous layer, the latterlayer was further extracted with ethyl acetate (20 ml×2) and the ethylacetate layers were combined. The combined ethyl acetate layer wasserially washed with 5% sodium hydrogencarbonate solution (20 ml), water(20 ml) and saturated aqueous solution of sodium chloride (20 ml) in theorder mentioned and dehydrated over anhydrous sodium sulfate. Thesolvent was then distilled off under reduced pressure and the residualcrude product was purified by silica gel column chromatography, elutionbeing carried out with hexane-ethyl acetate-ethanol (45/50/5, v/v/v).From the fraction containing the objective compound, the solvent wasdistilled off under reduced pressure to provide the following compound(116.2 mg).

The various physical constants of this objective compound were inagreement with the corresponding values mentioned in WO 93/19053.

¹H-NMR (CDCl₃; δ): 0.64-1.10 (24H, m), 1.20-2.00 (18H, m), 2.62-3.21(24H, m), 3.76-3.95 (8H, m), 4.41-4.57 (m) & 5.01-5.72 (m) (8H), 6.82(4H, d), 7.13 (4H, d)

What is claimed is:
 1. A compound of the formula:

wherein R₁ represents hydrogen or a hydroxyl-protecting group; R₂represents a carboxyl group or a protected carboxyl group; R₃, R₄, R₇and R₈ each represents methyl or benzyl substituted by morpholino; R₅,R₆, R₉ and R₁₀ each represents isobutyl or a salt thereof.
 2. Thecompound or its salt according to claim 1 wherein R₃ and R₇ eachrepresents benzyl substituted by morpholino and R₄ and R₈ eachrepresents methyl.
 3. A process for producing a depsipeptide derivativeor its salt characterized by subjecting a compound of the formula:

(wherein R₁ represents hydrogen or a hydroxyl-protecting group; R₂represents a carboxyl group or a protected carboxyl group; R₃, R₄, R₇and R₈ each represents a lower alkyl group, an aryl group or asubstituted or unsubstituted aralkyl group; R₅, R₆, R₉ and R₁₀ eachrepresents a lower alkyl group) or a reactive derivative of its carboxylgroup, or a salt thereof, to cyclization reaction to give a compound ofthe general formula:

(wherein R₃, R₄, R₇ and R₈ each represents a lower alkyl group, an arylgroup or a substituted or unsubstituted aralkyl group; R₅, R₆, R₉ andR₁₀ each represents a lower alkyl group) or a salt thereof.
 4. Theprocess of claim 3, wherein R₃, R₄, R₇and R₈ each represents methyl orbenzyl substituted by morpholino and R₅, R₆, R₉ and R₁₀ each representsisobutyl.
 5. The process of claim 4, wherein R₃ and R₇ each representsbenzyl substituted by morpholino and R₄ and R₈ each represents methyl.